The present invention relates to telecommunication systems and, more specifically, to a method and apparatus for switching between data communication channels having different bandwidths. The invention provides a means for switching between a low bandwidth channel and a high bandwidth channel in response to the bandwidth needs of the user. The means for switching is designed to avoid a thrashing problem that may be caused by some data inputs.
Switched data communication service has evolved from the low-speed modems of the early 1980s to current high-speed modems such as a V.34 modem and 56 K products. In addition to modems, switched digital service such as DDS service and basic rate ISDN service is now available from service providers. The data bandwidth or bandwidth for the above products is between 1.2 Kbps and 128 Kbps. Early data communication products used the analog PSTN where the data rate was dependent of the characteristics of the channel. Current ISDN service units typically have 1 D channel and 2 B channels where the D channel has a 16 Kbps bandwidth and the B channels have a 64 Kbps bandwidth.
In Basic Rate ISDN (xe2x80x9cBRIxe2x80x9d) service the D channel is always connected between the user and the central office switch. The low bandwidth D channel is used to send signaling information and packet data, such as X.25 packets. The B channels, B1 and B2, are used to provided data and voice services when coupled to the appropriate equipment at the customers premise. The B channels provide high bandwidth service and typically have a cost structure proportional to use. Because the D channel cost has a low fixed monthly cost it is desirable to use the D channel whenever possible. A typical data communication device at a customer premise is an ISDN service unit, such as an Adtran Express XR, Express XRT, Express XL, or Express XLT may be used for connection for BRI service.
It has been determined that a cost effect use of BRI is an Always On/Dynamic ISDN (xe2x80x9cAO/DIxe2x80x9d ) architecture. The AO/DI architecture is described in a white paper by Kuzma in a November 1996 contribution to VIA (Vendors ISDN Association). AO/DI is a networking service that provides packet service on the low bandwidth D channel and only uses a high bandwidth B channel upon user request. A method for determining when to make a user request is not discussed by Kuzma.
An invention described in U.S. Pat. No. 5,615,213 of Allan Griefer provides a means for implementing AO/DI. The Griefer invention is based on both message length and send queue length for switching to a B channel while operating in the packet mode of the D channel. Griefer does not provide directions for going from the B channel back to the D channel. Further Griefer does not consider the thrashing problem, frequent switching back and forth between the D channel and B channel, that may occur with certain data conditions.
Hence there is a need for an improved method and apparatus for providing AO/DI service. Such a method and apparatus should avoid the thrashing problem and maximize the benefits of AO/DI service. Further the method should be cost effective and have parameters that may be changed to meet the needs of individual users.
In accordance with the present invention these needs and objectives are successfully addressed by a new and improved method and apparatus, which is operative to controllably switch between a first communication channel, such as a low bandwidth ISDN D channel, and a second communication channel, such as a higher bandwidth ISDN B channel, in dependence upon lengths of time that average percentages of transmit and receive bandwidth satisfy prescribed threshold relationships. The D channel is always on, while one or both of the B channels becomes operational upon a request from the user. The invention uses the D channel and controllably switches to one or more B channels when necessary.
With the D channel providing data service, then in response to a sample timer timing out at a predetermined sample time, an average transmit rate is determined by dividing the number of bytes transmitted by the value of the sample time. The average receive rate is then determined by dividing the number of bytes received by the value of the sample time. The average percentage xe2x80x98transmitxe2x80x99 bandwidth is determined by dividing the average transmit rate by the bandwidth available, and the average percentage xe2x80x98receivexe2x80x99 bandwidth is determined by dividing the average receive rate by the bandwidth available. For typical D channel usage, the bandwidth available is 14 Kbps out of the 16 Kbps of the D channel.
Switching from the low bandwidth D channel to a higher bandwidth B channel occurs, if either of the average percentage transmit bandwidth or the average percentage receive bandwidth exceeds a prescribed upper threshold, and a bandwidth increase timer has expired. The bandwidth increase timer is used to prevent frequent and uncalled-for switching to the B channel and has a user presetable expiration value.
To determine whether the higher bandwidth condition demand has subsidedxe2x80x94allowing return to the D channelxe2x80x94the average percentage transmit bandwidth is compared with a lower threshold, less than the upper threshold. Switching back to the low bandwidth D channel from the higher bandwidth B channel occurs, if the average percentage bandwidth drops below the lower prescribed upper threshold, and a bandwidth decrease timer has expired. Similar to the bandwidth increase timer, the bandwidth decrease timer is used to prevent frequent and uncalled-for switching back to the D channel from the B channel and may be preset by the user. The combination of the actions of the bandwidth increase timer and the bandwidth decrease timer prevent a frequent back and forth switching referred to as thrashing.